1. Field of the Invention
The present invention relates to a current-perpendicular-to-plane (CPP) magneto-resistive element in which currents are fed in a direction perpendicular to a film plane, such as CPP giant magneto-resistive (GMR) element and tunneling magneto-resistive (TMR) element.
2. Description of the Related Art
Magneto-resistive elements have been used, for example, in the field of magnetic recording as a read element for reading recorded data from a magnetic recording medium. Reading of magnetic data can be performed by feeding a sense current to a magneto-resistive film through a prescribed current feeding structure and detecting change in sense current corresponding to change in resistance depending on external magnetic field.
CPP (current-perpendicular-to-plane) type has been known as one current feeding structure for feeding a sense current to a magneto-resistive element. In the CPP type, magnetic shielding films are disposed to hold a magneto-resistive film therebetween in a vertical direction perpendicular to the film plane and a sense current is fed to the magneto-resistive film through the magnetic shielding films (as disclosed in Japanese Unexamined Patent Application Publication No. 2003-17781).
In magneto-resistive elements, the MR ratio can be dramatically improved by using a half-metallic material with high spin polarizability (as exemplified by Heusler alloy) for a free layer or a pinned layer and using MgO as a crystalline material for a barrier layer. In order to improve the MR ratio as above, furthermore, it is required to perform high-temperature annealing at a temperature equal to or greater than 300° C.
In CPP magneto-resistive elements, however, high-temperature annealing at a temperature equal to or greater than 300° C. may grow crystal grains within the magnetic shielding film, decreasing the magnetic permeability, which impairs the magnetic shielding effect.